In recent years, systems which make a plurality of nodes existing in a network operate in a coordinated manner have been used. In such a network, it is important to synchronize times of a master node and a slave node with each other.
Synchronization of time between a plurality of nodes is carried out based on a clock synchronization protocol which uses Ethernet (registered trademark) frames and is defined in, for example, IEEE1588v2 or the like. However, when the clock synchronization protocol is used, precision of the time regenerated in a communication environment with large delay fluctuation may deteriorate. In addition, accuracy of the regenerated time may also deteriorate due to asymmetry of delays.
The Best Master Clock Algorithm, in which a node is selected to synchronize with by using Clock Quality or the like, which is communicated by a master node with Announce Message, is widely known. However, because the algorithm selects a node based on only precision and accuracy of a master node, influence from delay fluctuation and delay asymmetry on the network cannot be avoided.
In PTL 1, a clock synchronization system is disclosed which accomplishes clock synchronization between a master and a slave without using a boundary clock in a network including, in a portion thereof, asymmetric paths of forward and return transmission paths.
In PTL 2, a correction method is disclosed which corrects an inaccurate temporal synchronization which takes place due to an asymmetric delay in a communication link.
In PTL 3, a clock synchronization system is disclosed which, between a master node and a slave node, computes a difference between the times of the master node and the slave node based on a queuing delay which takes place on a communication message and synchronizes the time of the slave node with the time of the master node.